Electrolytic image eraser



June 20, 1967 D, J. J. LENNON ELECTROLYTIC IMAGE ERASER Filed April 15, 1965 W W W ATTO RN EYS United States Patent 3,326,793 ELECTROLYTIC IMAGE ERASER Donald J. J. Lennon, Acton, Mass, assignor to The Carters Ink Company, Cambridge, Mass., a corporation of Massachusetts Filed Apr. 15, 1963, Ser. No. 272,925 3 Claims. (Cl. 204224) My invention relates to image erasers, and particularly to a novel eraser for removing images which are composed of electrophoretically mobile material.

A method of producing images composed of dye particles which are electrophoretically mobile in solution is described in the copending application Serial No. 152,579, now US. Patent 3,145,156, filed Nov. 15, 1961, by Gerald Oster for Electrophoretic Printing, and assigned to the assignee of my application. This application also describes a number of electrophoretically mobile imaging materials suitable for electrophoretic deposition. It is the object of my invention to faciliate the erasure of dried images formed in this manner, to simplify correction and revision and the like, Without the abrasion of the image sheet caused by conventional image er-asers.

Briefly, an image eraser in accordance with my invention comprises a stylus consisting of two electrically insulated juxtaposed electrodes. At least one of the electrodes is made of a porous material by a reservoir connected thereto. The other electrode may be made in the same manner, or it may be made of a solid conductive material, depending on the imaging material to be erased. Means are stylus in convenient operating position in one hand, and this means preferably comprises a battery housing in which a battery of electrical cells is enclosed. Means are provided for connecting the battery across the electrodes, to provide an electrical potential between them. When the tip of the stylus so formed is applied to a substrate such as paper bearing an image to be erased, the electrolyte in the porous electrode or electrodes dampens the surface of the substrate, forming a fluid field in which the image particles may move under the influence of the potential between the electrodes. The particles so moved are drawn to the appropriately charged electrode, which should be porous so that the image forming particles are drawn into the pores of the electrode and removed entirely from the paper.

Since the pH of the paper in the vicinity of each electrode is aflected, one electrode creating a zone of high pH and the other a zone of low pH, imaging materials which may be erased by exposure to a predetermined pH are also erasable by the apparatus of my invention. In addition, oxidizing and reducing zones exist adjacent the electrodes, such that imaging materials which may be erased by either oxidation or reduction can be removed by exposure to a selected electrode. Preferably, when constructed in accordance with my invention for this purpose, the inner stylus electrode is made porous, and the battery is polarized so that the desired erasing action will take place adjacent the outer electrode, so that the opposite effect produced by the inner electrode will not restore the erased image.

The apparatus of my invention will best be understood in the light of the following detailed description, together with the accompanying drawings, of various illustrative embodiments thereof.

In the drawings: I

FIG. 1 is an elevational view, with parts shown in crosssection and parts omited to avoid repetition, of an image eraser in accordance with a preferred embodiment of my invention;

FIG. 2 is a cross-sectional view of a modification of wettable by an electrolyte provided for holding the a 3,326,793 Patented June 20, 1967 the apparatus of FIG. 1, with parts shown in cross-section and parts broken away; and

FIG. 3 is a schematic representation of another embodiment of my invention, with parts broken away and parts shown in cross-section.

Referring first to FIG. 1, I have shown an image eraser in accordance with one embodiment of my invention which comprises an outer cylindrical conducting case 1, of metal or the like, into which a cylindrical body-liner tube 2, of any suitable insulating material such as polyethylene or the like, is slidably received. Housed in the liner 2 is a battery consisting of a desired number of electrical cells 3. While any suitable battery may be employed, in accordance with one embodiment of my invention, the battery consisted of eighteen cells 3, each of which was a mercury cell having a potential of 1.4 volts.

The upper portion of the body liner 2 is formed with a flange 4, which retains a spring 5, of metal or the like. The spring 5 engages the positive terminal 6 of the uppermost cell 3, and holds it out of engagement with the protruding end of a metal spring 7. The metal spring 7 makes contact at the sides of the conducting case 1, and is actuable to make contact between the case and the negative terminal of battery 3 by movement of a pushbutton 8, which may be made of any suitable material such as metal, plastic, or the like. By this arrangement, depression of push-button 8 will cause an electrical path to be completed between the negative terminal 6 of the uppermost cell 3 and the case 1.

The positive terminal 8 of the lowermost cell 3 engages a conducting button formed on a contact lead 10, of metal wire, the metal wire 10 being embedded in a non-conductive support such as the head 11, which may be made of any suitable non-conducting material; for example, it may be made of one of the well known epoxy resins widely employed as cements. A threaded shell 12, of metal or the like, surrounds and holds the supporting head 11, and is threaded into an adapter 13, of metal or the like, which is in turn held by threads 14 formed at the lower end of the case 1. Also threaded to the threads 14 on the case 1 is a non-conducting receptacle 15 of annular shape, which may be made of any suitable non-conducting material.

Within the receptacle 15 is an annular nozzle 16, of any suitable insulating material such as polypropylene or the like. The nozzle 16 is provided with a central aperture which retains a porous electrode formed by a porous insulating material containing an electrolyte, such as a solution of sodium chloride and water. As here shown, the porous material comprises a bundle of non-conducting fibers 18 which may be of polyacetate resin or the like, and which are small enough so that the inerstices between them have capillary properties. A supply of electrolyte to the porous electrode so formed is provided by a sponge 17 saturated with electrolyte. As shown in FIG. 1, the base of the contact lead 10 is coiled to increase the area of contact with the sponge 17.

Disposed about the outer end of the non-conducting nozzle 16 is an annular conductive electrode 19, which may be of any suitable conducting material such as metal, but preferably is made of a conductive plastic, such as polyvinvyl chloride filled with conductive particles. This electrode .is connected to the metal case '1 by means of a metal spring wire 20, which is coiled about the annular electrode 19 and is secured at its other end to the case, as by welding, soldering, brazing or the like. If it is desired to make the parts removable, the spring 20 may simply be coiled in the threads 14 on the case 1.

The image erasing unit of FIGURE 1 is shown with its erasing stylus adjacent a substrate 21, of paper or the like, upon which an image is assumed to be formed. Assuming that the image is of electro- 3 phoretically mobile particles, it may be erased in the manner next to be described. First the pushbutton 8 is depressed with the thumb while the case 1 is held in the fingers of one hand; the stylus is placed on the substrate in the position shown. Electrolyte from the porous electrode comprising a fibers 18 is drawn out into the pores of the substrate, being replenished from the sponge 17. As the substrate is dampened, an electric circuit is completed between the electrode 19 at the potential of the negative terminal of the battery, and the lead 10, at the potential of the positive terminal of the battery through a path comprising the portion of the substrate dampened by the electrolyte, the porous electrode 18, and the reservoir 17. The dampening of the substrate causes the image particles to become mobile, and they are attracted to the electrode opposite the charge which they bear. For example, with the apparatus connected as shown, if the image particles were so charged as to migrate toward the positive electrode, they would flow up into the interstices in the porous electrode comprising the fibers 18. If it is desired to erase an image of electrophoretically mobile dye particles which would migrate toward the negative electrode, the battery cells in the liner 2 could simply be inverted to provide the opposite polarity, so that the particles would always be removed by migration into the porous electrode. The area of the porous electrode should not be too large with respect to the area of the nonporous electrode 19, or the field gradient through the dampened substrate will be unduly small. In other words, since the battery voltage is divided between the porous cylinder formed by the dampened fibers 18, the reservoir 17, and the dampened substrate, the resistance of the latter should be a significant proportion of the total resistance. Of course, the voltage across the substrate should be kept sufficiently low to avoid burning the paper.

Referring now to FIGURE 2, I have shown a second embodiment of my invention in which the outer electrode of the stylus is made porous, while the inner electrode is of solid conductive material. In FIGURE 2, parts corresponding to the parts of the apparatus in FIGURE 1 are given similar reference characters, and the portions not shown may be assumed to be identical to the corresponding parts of the apparatus of FIGURE 1. The apparatus is the same as that in FIGURE 1, with the exception of the erasing stylus. As shown in FIGURE 2, the modified stylus comprises an outer annular receptacle 22 of nonconducting material, such as plastic or the like, .which is provided at its upper periphery with threads mating with the threads 14 on the metal case 1. Within the receptacle 22 are an annular insulating member 23, an electrolyte reservoir comprising an annular sponge 24, and a coiled metal conducting lead 25, the latter being coiled upon itself at one end to engage the upper surface of the reservoir 24, and connected at its other end, as by welding, brazing, soldering or the like, to the metal case 1. Surrounding the annular insulating member 23 is an outer porous electrode 26 of any suitable porous material such as felt or the like, which becomes filledwith electrolyte from the reservoir 24 to form a conducting electrode.

Within a central bore in the annular insulating member 23 is a solid cylindrical electrode 27, which is provided at its upper end with a flange 28 to make contact with the coiled lower portion of the contact lead 10.

The operation of this embodiment of my invention is essentially the same as that described above in connection with the embodiment of FIGURE 1, except that the porous electrode is now on the outside of the stylus. When the cells 3 are poled as shown, this will be the negative electrode. This arrangement is suitable for erasing electrophoretically mobile images which migrate to the negative pole. This arrangement might be preferred for some purposes to the construction of FIGURE 1, because the area being erased is at the edge of the stylus, rather than being within the body of the stylus tip as in the embodiment shown in FIG. 1.

In connection with images which can be erased by oxidation, reduction, or pH adjustment, it should be pointed out that in the region of the substrate near the positive electrode, oxidation will take place, and the pH will be acidic. Under the negative electrode, the pH will be basic, and reduction will take place. Accordingly, images made of any material which can be erased by oxidation, reduction or pH adjustment can be easily erased by the appa- Iatus of my invention. In constructing the apparatus for erasures of this kind, the battery should be polarized so that the desired erasing reaction will take place under the non-porous electrode. The reason for this preferance is that, referring to FIG. 1 for example, ions of one polarity are created in the reservoir 17 near the point of contact with the lead 10, and ions of the opposite polarity are created in the substrate 21 near the surface of the nonporous electrode 19. These ions migrate towards each other, meeting and neutralizing somewhere in the porous core 18. Thus, only those ions found in the vicinity of the non-porous electrode are available for erasing action in the substrate. The resistance of the porous electrode relative to that of the dampened substrate is not significant when oxidation or reduction reactions, or pH adjustment, are relied on for erasure. For use with certain imaging materials, it may be desirable to choose an electrolyte having specific solvent properties. For example, conventional ball inks will be more readily erased if a solvent for the ink, such as acetone, methyl alcohol, or the like, is used on the electrolyte.

Referring now to FIG. 3, a third embodiment of my invention is schematically illustrated. In this embodiment,

the battery, shown schematically at 29, may be composed of cells as in FIGS. 1 and 2 or may be any other desired source of D.C. potential.

A double-pole, double-throw switch 30 is provided for applying the potential of the battery across a first pair of terminals a and b, or, in an opposite sense, across the terminals c and d. Terminals a and d are connected in parallel to an outer annular porous electrode 31, and the terminals b and c are connected in parallel to an inner porous electrode 32. As in the previous embodiments, these electrodes are maintained with their ends in juxtaposed relationship and mutually insulated by an annular spacer 33 of non-conducting material. The specific structural details of the practical embodiment might combine the features of the styli shown in FIGS. 1 and 2, with the inner electrode being made porous as shown in FIG. 1 and the outer electrode being made porous as shown in FIG. 2. With both electrodes made of porous material filled with a suitable electrolyte, charged particles may be caused to migrate into either electrode by suitably actuating the switch 30 to apply the proper potential to the desired electrode to attract the dye particles of an electrophoretically mobile image. With a given polarity, the electrophoretic erasing process can be expedited by making the porosity of the electrode to which the dye particles are attracted more porous than the other electrode. Of course, this expedient would only be useful with one polarity connection of the electrodes for a given imaging material.

While I have described various embodiments of my invention in detail, many changes and variations will occur to those skilled in the art upon reading my description, and such can obviously be made without departing from the scope of my invention.

Having thus described my invention, what I claim is:

1. Apparatus for erasing an image composed of electrophoretically mobile material lying on a surface, comprising a tubular casing, an era-sing head coaxially positioned at one end of the casing, means at least partially closing the other end of the casing; a transverse partition extending across the casing adjacent the inner end of said erasing head to provide a battery receiving chamber separated from said erasing head; and a manually-actuable switch located in the wall of said chamber; said erasing head comprising a pair of electrodes, one being central and coaxial with the casing and the other being tubular and closely surrounding said central electrode but separated therefrom by electrical insulation, the outer ends of the electrodes and insulation being substantially coplanar and approximately concentric, at least one of said electrodes being porous and normally saturated with a liquid electrolyte; first electrical lead means extending through said partition and in electrical contact with said central electrode; second electrical lead means extending from said tubular electrode to the casing; said battery chamber being adapted to hold the battery with one electrode thereof in contact with said first electrical lead means, and said switch being adapted to connect the casing and thus the tubular electrode with the other battery electrode.

2. Apparatus for erasing an image composed of electrophoretically mobile material lying on a surface, comprising a holder, an erasing head attached to the holder, a double pole double throw switch mounted on the holder and connected to the erasing head, and a battery connected to the switch; said erasing head comprising a porous tubular outer first electrode, a tubular insulating element within the first electrode, and a porous second electrode within the insulating element, the first and second electrodes being concentric, and having their outer ends adjacent and coplanar, each electrode being saturated with an electrolyte; said switch being connected so that in one switch position the first electrode is connected to the positive pole of the battery with the second electrode connected to the negative pole of the battery, and in the other switch position the second electrode is connected to the positive pole of the battery with the first electrode connected to the negative pole of the battery.

3. An image eraser, comprising a case; connectors within said case adapted to be energized by a DC. potential; an erasing stylus mounted on said case, said stylus comprising an annular electrode of conductive material, an annular insulator concentric with and within said annular electrode, and a second electrode within said annular insulator, the second electrode comprising a column of elongated fibers of insulating material arranged in parallel relationship to each other to provide elongated interstices therebetween, a compressible porous fluid reservoir contacting said bundle at one end, and an electrolyte contained in the reservoir and said interstices; and switch means on said case for electrically connecting the electrodes in series with said connectors; the outer ends of said electrodes being coplanar whereby, when said ends are placed on a surface bearing electrophoretically mobile material and said DC potential is connected to said electrodes, the electrolyte dampens said surface and said material moves from said surface to an electrode.

References Cited UNITED STATES PATENTS 2,275,281 3/1942 Berl 204-284 2,365,539 12/1944 Flowers 204-443 2,498,129 2/1950 Lindsay 204-424 2,540,602 2/1951 Thomas et a1. 204-224 2,798,849 7/ 1957 Lindsay 204224 FOREIGN PATENTS 1,228,817 3/1960 France.

469,437 7/ 1937 Great Britain.

362,768 9/1938 Italy.

JOHN H. MACK, Primary Examiner. .W. VAN SISE, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3, 326, 793 June 20, 1967 Donald J. J. Lennon It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 30, for "8" read 9--; line 52, stices" read interstices for "ine1 Signed and sealed this 2nd day of January 1968.

(SEAL) Attest:

EDWARD J. BRENNEE Edward M. Fletcher, J r.

Commissioner of Patents Attesting Officer I 

1. APPARATUS FOR ERASING AN IMAGE COMPOSED OF ELECTROPHORETICALLY MOBILE MATERIAL LYING ON A SURFACE, COMPRISING A TUBULAR CASING, AN ERASING HEAD COAXIALLY POSITIONED AT ONE END OF THE CASING, MEANS AT LEAST PARTIALLY CLOSING THE OTHER END OF THE CASING; A TRANSVERSE PARTITION EXTENDING ACROSS THE CASING ADJACENT THE INNER END OF SAID ERASING HEAD TO PROVIDE A BATTERY RECEIVING CHAMBER SEPARATED FROM SAID ERASING HEAD; AND A MANUALLY-ACTUABLE SWITCH LOCATED IN THE WALL OF SAID CHAMBER; SAID ERASING HEAD COMPRISING A PAIR OF ELECTRODES, ONE BEING CENTRAL AND COAXIAL WITH THE CASING AND THE OTHER BEING TUBULAR AND CLOSELY SURROUNDING SAID CENTRAL ELECTRODE BUT SEPARATED THEREFROM BY ELECTRICAL INSULATION, THE OTHER ENDS OF THE ELECTRODES AND INSULATION BEING SUBSTANTIALLY COPLANAR AND APPROXIMATELY CONCENTRIC, AT LEAST ONE OF SAID ELECTRODES BEING POROUS AND NORMALLY SATURATED WITH A LIQUID ELECTROLYTE; FIRST ELECTRICAL LEAD MEANS EXTENDING THROUGH SAID PARTITION AND IN ELECTRICAL CONTACT WITH SAID CENTRAL ELECTRODE; SECOND ELECTRICAL LEAD MEANS EXTENDING FROM SAID TUBULAR ELECTRODE TO THE CASING; SAID BATTERY CHAMBER BEING ADAPTED TO HOLD THE BATTERY WITH ONE ELECTRODE THEREOF IN CONTACT WITH SAID FIRST ELECTRICAL LEAD MEANS, AND SAID SWITCH BEING ADAPTED TO CONNECT THE CASING AND THUS THE TUBULAR ELECTRODE WITH THE OTHER BATTERY ELECTRODE. 